Electron gun construction



Oct. 17, 1961 E. GRIFFITHS ELECTRON GUN CONSTRUCTION Filed July 16, 1959INVENTOR LE/GHTON E. GRIFFITHS ATTORNEYJ 3,035,123 ELECTRON GUNUNSTRUCT1ION Leighton E. Grifiths, Pomptou Lakes, NJ, assignor toGrifiiths Electronics, inc, Newark, N..l., a corporation of New JerseyFiled July 16, 1959, Ser. No. 827,532 4 (Ilaims. (Cl. 313-82) Thisinvention relates to electronic apparatus and more particularly toelectron emitters for cathode ray tubes.

It is the basic object of the present invention to provide an improvedand new form of electron emitting device particularly useful in theso-called electron gun of cathode ray tubes of the television type.

More specifically it is an important object of this invention to providean arrangement in an electron emitter providing for a simpler assemblywhile holding close tolerances between the actual emitting surface andthe apertured area of the number one grid.

An important object of the invention resides in the construction of theelectron emitter assembly whereby leakage across the insulation whichsupports the cathode sleeve from the grid cylinder is materially reducedby the provision of shadowed areas thereon.

Another important object of the invention comprises the mounting of thecathode cylinder in its ceramic support disc so that a large percentageof its length extends above the disc and only small percentages areincased in the disc or extend below it, whereby heat loss is kept to aminimum, and evaporation and sublimation, which cause current leakage,cannot occur in critical areas.

Still other objects and features of the invention include, simplifiedassembly procedure, close tolerances where critical, low mass and costof components and improved operating efficiency.

Further features and objects of the invention will be more apparent tothose skilled in the art upon a review of the following specificationand accompanying drawing wherein is disclosed a single exemplaryembodiment of the invention, it being understood that such variationsand modifications may be made therein as fall within the scope of theappended claims without departing from the spirit of the invention.

In said drawing:

FIG. 1 is a side elevation of an electron gun construction in accordancewith the present invention, shown in position in the neck of atelevision type of cathode ray tube, the neck being shown broken awayfor clearer illustration; and

FIG. 2 is a longitudinal, central section through the grid cylinder,grid tube insulator, cathode tube and cathode assembly illustrating theimportant features of the invention on an enlarged scale.

The television set version of a cathode ray tube, in the vernacular apicture tube, includes an elongated neck housing one or more so-calledelectron guns each adapted to direct a concentrated beam or ray ofelectrons toward the fluorescent viewing screen at the front of thetube, to produce the desired picture effect after proper vertical andhorizontal deflection, as well understood.

Extreme care in the design and construction of the electron gun iscalled for if long life, satisfactory performance and high eiliciencyare required. Fine tolerances for the assembly of certain of the partsare required and unusual shaping and relationship of some of thecomponents is essential to assure the fulfilment of the rigidrequirements set forth above and others as will later appear. Thepresent invention is concerned with such construction, arrangement andassembly of these parts to insure more efficient electron emission, itscontrol as to direction and beam concentration, and insurance againstleakage across the cathode supporting insulator.

areas Fatented Get. 17, 1961 Reference should now be had to FIGURE 1 fora general disclosure of the neck and connection base section of apicture tube fitted with an electronn gun, the number one grid andcathode assembly of which is constructed in accordance with the presentinvention. In this figure, 10 represents the glass wall of the tube neckfitted with the usual base 11 mounting the conventional arrangement ofcontact pins and central orienting plug, all as is generally known.

Within the neck and supported from conductor and pillar wires arrangedin the tube press is the assembly 12 generally referred to as anelectron gun, .including, among other things, a cathode, cathode heater,the number one grid, one or more additional grids and one or more anodesarranged generally in the order named and longitudinally of the tubeneck starting from the base. The several components are mechanicallyconnected together by suitable mountings and attachments tolongitudinally directed ceramic rods 13, while the top disc 14- isfitted with radially disposed spring fingers l5 engaging the walls ofthe neck for stabilizing and centering the gun assembly therein. This ismore or less conventional construction and may be varied to suitparticular situations or the dires of the individual tube manufacturer.

The cathode, the number one grid and the insulator mounting the formerfrom the latter compose the subassembly forming the subject matter ofthe present invention and this is shown in greater detail and on alarger scale in FIGURE 2 and designated 16 in both figures.

The main component of the sub-assembly 16 is the large diameter gridcylinder 18 drawn from appropriate metal of relatively thin gauge andhaving the straight cylindrical wall extending upwardly from the openbottom 19, normal to the axis of the cylinder, to the curved junction2%} between the sidewall and the flat annulus 21 partially closing theupper end of the grid cylinder.

The inner edge of the annulus meets at 22 and is integral with thecylindrical wall 23 of the grid tube having the integral fiat topclosure 24, centrally perforated as at 25 by a circular aperturepermitting egress of the beam or ray of electrons generated by theheated cathode for impingement on the fluorescent viewing screen(notroviding a ring or bead 28 protruding downwardly from' its undersurface whereby to separate the fiat upper face 31 of the ceramic orinsulating disc 31 from the main area of the annulus. This disc iscylindrical and its sidewall 32 is such as to fit with reasonablecloseness within the wall 18 of the grid cylinder. The ceramic disc orinsulator is held in position against bead 28 by having the perimeter ofits flat lower face 33 engaged by the inturned flange 34 formed integralwith the short skirt 37 welded to the wall of cylinder 18 while beingheld tightly against the under face of the ceramic disc. Obvious- 1yother securing means such as a bead rolled into the wall of cylinder 13,or prongs or tabs bent inwardly therefrom to engage the under face ofthe disc would be optional.

The ceramic insulating disc is unique in construction as will be seenfrom FIGURE 2 for it is provided with a deep, large diameter well 49extending therein from the upper surface and having a flat bottom 41spaced reasonably close to the under surface of the disc. The top face34) of the disc is spaced below the annulus 21 by virtue of head 28, butthe inner cylindrical wall 42 of the well 4*) extends up and partiallyinto the grid tube 23 where it is defined by the relatively thin,annular wall 43 extending upwardly from the surface 30 and formedintegral with disc 31. The outer cylindrical surface 44 of wall 43 isshown to be spaced radially from the inner wall of sponges the grid tube23.by.the clearance 45, only large enough to prevent contact andpossible electrical leakage.

The cathode tube, which is adapted to receive and housetheheatercomprises. an open end metal cylinder 47 passing through acylindricalaperture 48 in the relatively thin wall between the bottom 41 of thewell and the bottom face ofthe ceramic disc. The wall of aperture d8 hasa close fit to the outer diameter of the cylinder. The well all may beconsidered as a counter-bore for aperture or bore 48.

The cathode tube is assembled inthe ceramic prior to the latter beingsecured in the grid cylinder 38 and the procedure is preferably asfollows. A bead such as that illustrated ,at 49 is rolled on thecylinderto limit its extensionthrough aperture 43 when it is inserted throughthe well. An alternative means would be to weld a flangev or rim inplace of head 49. When the cylinder 4'7 is properly positioned with thisbead against the bottom 41 of the well, the second bead 51% is rolledagainst the underface 33 ofthe disc to lock the cathode tube firmly in,positionand, then, preferably the lower end of the tube is slightlyflared. as at Slto facilitate the insertion of the heater assembly.

The. arrangement just described is such that approxi mately seventypercent of the cathode cylinder extends above the well bottom 41 andapproximately ten percent protrudes beneath. the lower face of theceramic disc whereby very little heat loss results and no evaporation orsublimation. is effected by the lower protruding portion which, mightcause leakage. between the cathode and the grid. However, enough of thecylinder protrudes bencath the disc to allow welding the cathode tab 54thereto as. shown. Heat loss is particularly critical in cases wherethe. cathode cylinder is ofsrnall diameter and low current heaters are.used. Any substantial heat loss might well shortenthelife of the,cathode ray tube by reducing emission as. .efliciency falls.

The. cathode cylinder 47 may. be drawn with an integral' closed head ifdesired, but. it is preferably to close the upper end by means. of atelescoped metal cap 56 as shown. This has several advantages, amongwhich may be mentioned. the selection of a superior metal which can beused in lesser quantity, a choice of thickness and a better flatteningof the actual closure head 57 and, finally, the possibility of moreaccurately adjusting the spacing between the front surface 3% of theceramic disc and the face of the closure head 57 prior to welding itinto the position shown. This permits a very accurate control of thespacing of head 57 from head 24' which is essential for proper beamcontrol. As shown, the head 57 is covered with coating. 59. of. anemissive material, the composition of which. is open to choice and manyare well-known.

Although the majoremission takes place from the coating 59, the metal ofthe tube47 and of the cap 56 is heated, at least during processing priorto and during evacuation, to such a temperature that there is a certainamount of evaporation and/or emission from their outer surfaces whichmight so coat the upper face 3-3 and the walls of the well 49 as toproduce a substantial degree of current leakage betwen the cathodecylinder and the number one grid cylinder 18 where its head 28 engagesthe face 39.

This type of loss is substantially eliminated by the presentconstruction, first by forming the deep well dil which increases thepath between the two metal surfaces over that which would exist if thewell were not in existence, and, secondly, the collar or protective wall43 extends upwardly to intercept any evaporation or emission from anyarea of the cathode cylinder and completely shadow out or protect thetop surface 3% of the ccramic. The outer surface of wall 43 is alsoprotected against coating. The clearance 45 betwen the wall 43 and theinner surface of grid tube 2.) is so adjusted in respect to the heightof the wall that no straight path exists from the highest point on thecathode cylinder or its cap to. any of the area of the disc surface 3twhereby insulation resistance remains high.

It will be appreciated that adjusting of the spacing of the head 57above the surface 30 of the ceramic disc may be effected by the use ofapparatus not substantially dilferent in form and operation from thatillustrated in FIGURE 5 ofthe patent to L. E. Grifiiths, 2,758,236granted August 7, 1956, and checking of this critical dis tance may beeffected on a dial gauge arrangement as illustrated in FlGURE 6 of thatpatent.

The assembled cathode cylinder and ceramic disc may be used in a moreconventional number one grid cylinder, which is of uniform diameterthroughout its height, by substituting for the annulus 2i. and thepositioning bead 27, the proper length tube or cylinder of metal flangedor footed if desired to rest on the surface Sill and having its otherend engaging the under surface of the full diameter closure of. the gridcylinder. Here the accuracy called forisinthe length of this spacerwhich not, only serves for dimensional control but shields the area ofthe disc outside of its perimeter from emissive material. In eitherassemblythere is always at least a shadowed area St just outside of thewall 43 due to the substantial- 1y lesser diameter of the cathode tubethan that. ofthe wall 4.3.

I claim:

1. A sub-assembly for use in the first grid cylinder of, a cathode raytube comprising, in combination, a thick disc of insulation materialsized to closely fit within the lower portionof said cylinder and havingsubstantially fiat'top and bottom: faces, a central bore through saiddisc, a. counterbore forming a well opening through the top face andhaving a .depth more than two-thirds the thickness of, the disc, asintegral wall above the top face having its inner surface coextensivewith the well wall, a cathode tube projecting through and secured insaid bore and having of the order of 10 percent only of its lengthdepending below said bottom face and of the order of 70 percentprojecting above the well bottom, and at least 25 extending above thetop of said wall.

2. A sub-assembly for use in a stepped diameter first grid cylinder of acathode ray tube having a flat annulus connecting the large and smalldiameter cylinders, in combination, spacer means on said annulus andremote from both diameters thereof projecting a predetermined distanceinto the large diameter cylinder, a single, thick disc of insulatingmaterial diametered to fit in said large 1 cylinder and having a flatupper face area engaging said spacer means, means on said cylindermaintaining the disc face against said spacer, a cathode tube extendingaxially through and secured in only said disc, a cap telescoped on theupper end of said tube adjusted so that its flat top. is. spaced apredetermined and substantial distance from said disc upper face, meansincorporated within said disc for extending the leakage path thereoverbetween the cathode tube and said spacer means, and upwardly extendingmeans integral with said disc shadowing an annular area of said discupper face against contaminationfrom said cathode tube.

3. For use in an electron gun for cathode ray tubes. in combination, anumber one grid cylinder having tandem arranged co axial, large andsmall diameter portions, one. about twice the diameter of the other, andan annular connecting portion, a perforated grid disc closing the remoteendv of the small diameter portion, integral spacing means on saidannular portion projecting towardthe remote end of the larger diameterportion. a single, thick insulating disc sized to lit into said largediameter portion and having a flat top engaged by said soacing means forpositioning said disc a fixed distance from the. flat, underface of saidannular portion, said disc having acentral aperture of less diameterthan said small. diameter portion of the grid cylinder and an open.topped well co-axial with said central aperture, a cathode tube fixed insaid aperture and having a closed end positioned close to saidperforated grid disc, said cathode tube projecting above the well bottomabout 70% of its length to radiate most of its heat above the insulationdisc, a radially thin annular barrier wall extending upwardly from saidinsulating disc, spaced from the cathode tube a distance substantiallyhalf of the tube diameter and entering said small diameter portion ofsaid grid cylinder and spaced but slightly from the inner wall thereof,said cathode cylinder extending substantially above the top of saidbarrier wall and the wall of said well and the inner wall of saidbarrier being co-extensive.

4. For use in an electron gun for cathode ray tubes, in combination, anumber one grid cylinder having tandem arranged co-axial, large andsmall diameter portions, one about twice the diameter of the other, andan annular connection portion, a perforated grid disc closing the remoteend of the small diameter portion, integral spacing means on saidannular portion projecting toward the remote end of the large diameterportion, a single thick insulating disc sized to fit into said largediameter portion and having a flat top engaged by said spacing means forpositioning said disc a fixed distance from the flat underface of saidannular portion, said disc having a central aperture of less diameterthan said small diameter portion of the grid cylinder and an open toppedwell co-axial with said central aperture, a cathode tube fixed in saidaperture and having a closed end positioned close to said perforatedgrid disc, radially thin annular barrier wall extending upwardly fromsaid insulating disc, spaced from the cathode tube a distancesubstantially half of the tube diameter and entering said small diameterportion of said grid cylinder and spaced. but slightly from the innerwall thereof, said cathode cylinder extending substantially above thetop of said barrier wall, the wall of said well and the inner wall ofsaid barrier being co-extensive, said closed end on said cathode tubecomprising a one-piece cap having a flat top and an integralcylinder-ical skirt telescoped over the cathode tube a distance adjustedto provide a predetermined spacing from the ceramic disc top to the captop whereby the cap top has a predetermined clearance from the underfaceof the grid disc for beam control.

References Cited in the file of this patent UNITED STATES PATENTS 202,712,087 Fite June 28, 1955 2,888,588 Dichter May 26, 1959 2,891,183Barnett June 16, 1959 FOREIGN PATENTS 887,684 Germany Aug. 27, 1953901,565 Germany Jan. 11, 1954

